Numerous drying devices are known and are used in a variety of industries. For example, dryers are commonly used to remove moisture from such mined materials as coal, bentonite, and other substances, particularly clay-like substances. Dryers are commonly classified in two different ways. First, dryers are either batch or continuous types. As the name implies, batch dryers remove moisture from an indentifiable accumulation of a substance before starting on the next accumulation. Continuous dryers operate to remove moisture from material from the moment it is introduced into the device until the moment it leaves the device with material constantly being introduced. Secondly, dryers are classified as either direct or indirect heat dryers. A direct heat dryer uses primarily convection to move a hot, dry gas through the dryer housing. An indirect heat dryer is designed to primarily use conduction or radiation for heating the substance so as to release moisture. Direct, continuous heat dryers show the greatest similarity to the present invention.
There are three commonly recognized conditions for the efficient drying of a substance with a direct heat dryer. In particular, (1) heat must be supplied under proper control; (2) there must be exposure of the wet surfaces of the substance to the drying medium as the substance is conveyed at a controlled rate through the drying apparatus; and (3) a continuous flow of gases must be exhausted for removal of vaporized moisture. Prior art devices do, of course, supply heat and show mechanisms for continually exhausting vaporized moisture. The devices differ in the provision of how wet surfaces of the substance are exposed to the drying medium.
A particularly popular direct heat dryer is called a rotary dryer. These mechanisms are generally massive cylinders which are rotated. The wet substance is introduced at one end. As the substance rotates with the cylindrical housing, it falls away from the side and back toward the bottom. Baffles are sometimes used to prevent the substance from falling away from the side too rapidly. If the substance cakes or otherwise sticks to the side of the cylindrical housing, knockers are installed to bang the side of the housing thereby shocking the wall so as to release the substance from the inner side. Alternatively, chains are attached to the inner wall. The wet substance rests on the chains so that as the cylindrical housing rotates, the substance is forced to fall away from the inner wall as the chains fall downwardly away from the wall.
Other drying mechanisms show the use of rotating shafts having paddles or other stationary stirring elements attached thereto. The stirring elements apparently mix the wet substance so as expose as much of the substance as possible to the drying medium.
The prior art, however, has not satisfactorily addressed the condition of providing maximum exposure of the wet substance to the drying medium. The problem is especially drawn into focus when observing entire industries building huge plants which simply grind a substance which has been previously dried into a cake-like aggregate.